1. Field of the Invention
This invention relates to reamer cutting heads for surgical reamers used to enlarge bone canals during orthopedic surgery. More particularly, this invention relates to a cutting head which is easily adapted for use with a surgical reamer having a flexible drive shaft.
2. Description of the Prior Art
Surgical reamers are used in orthopedic surgery to enlarge medullary canals of long bones such as the femur and humerus in preparation for insertion of fixation devices, performing an intramedullary osteotomy, stimulating bone growth, the insertion of a plug to preclude bone cement from migrating while it is in the viscous state, and for other reasons. The medullary canals of bones are seldom straight. More typically, the canal will have some degree of curvature to it.
Should a straight and rigid series of reamers be employed to enlarge the canal, there is considerable likelihood that the reamer, in not being capable of following the bone's curvature, will jam or will not remove the desired uniform amount of bone tissue. In such a situation excessive tissue removal occurs in at least one plane as a reamer advances. For this reason, medullary canals are almost always prepared with reamers having a flexible shaft. Generally reamers for use with a flexible shaft utilize a central bore through both the reamer and drive shaft. The central bore is intended to receive a long, small diameter guide pin which is initially inserted into the medullary canal to act as a track for the advancing reamer. However, the use of a flexible shaft does not always solve the problem of excessive tissue removal and jamming.
The prior art cutting head design contributes to the history of intramedullary reamers jamming during use in long bones. When this jamming occurs with the prior art cutting head, the long guide pin has to be withdrawn from its position to assist in dislodging the reamer cutting head. This can result in a loss of reduction at the fracture site. Heretofore, the shape of the reamer cutting heads has been basically a cylinder with a short angled area towards the front that would do the cutting and another short angled area at the back of the head that is intended to facilitate the removal of the reamer. Such a cutting head is shown generally in U.S. Pat. No. 4,706,659, which issued to Matthews et al on Nov. 17, 1987. U.S. Pat. No. 4,751,992, which issued to A. DiPietropolo on Jun. 21, 1988, shows a cutting head on a shaft but does not refer to the design of the cutting head.
The cylindrical shape of the prior art cutting heads results in long flutes that produce friction and considerable heat while turning. This heat can be detrimental to the bone. The shape can also result in the reamer cutting a larger hole than desired as the reamer is directed away from its intended path of cutting, as when cutting a curved canal. As the reamer tilts or cants with respect to the canal, it cuts in a diagonal plane rather than a plane perpendicular to the canal. When a cylindrical cutting head is canted with respect to the internal bore and cuts a larger diameter than desired, jamming is likely to occur.